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LM5118 over-current protection or other problem

Mario Paroni
Prodigy 185 points
Other Parts Discussed in Thread: LM5118

Hello,

I have a problem with the IC LM5118. I made the PCb similar to the lay-out of  the Evaluation Board with the components indicated by the AN-1819, for operate with a input from 5 to 75V and output at 12V with a load that can be from 0.1 to 3A.

I made three tipes of PCB very similar, all works except the final one, where happens this:

With a load more than 0.4A, if I give at the input a power greater than 15V the LM5118 remain in over-current protection and restarts only if I disconnect the load. If I give the input power lower than 15V the LM5118 works and I can increase the input voltage up to 75 volts without problems.

The three PCBs are virtually identical but the last also changing all components and the boards always generates this problem.

Can anyone help me?

Thanks a lot

  • 0
    TI__Mastermind 21720 points
    Hi Mario,

    You said the three boards are nearly identical. What are the differences between the three boards?
    Can you post your schematic?
    Can give me waveforms for the for both of the switch nodes and the inductor current during the fault condition?

    Just from the initial description I would check you sense resistor and you ramp capacitor (connected to the RAMP pin) and make sure that they are not damaged. It may also be some other miss populate part.


    Thanks,

    Garrett
  • 0 in reply to Garrett Roecker
    Prodigy 185 points

    Hello Garrett,
    I cut the line connecting the capacitor C21 to PIN 16 and I made sure that the path is shorter, in this mode works always. It 's very strange because the line in the other PCBs is also longer.

    Thanks,

    Mario